Network node with plug-in identification module

ABSTRACT

A network node includes a housing in which the electronics of the network node are contained, the housing having an external port to which a plug-in module can be physically attached. The plug-in module contains a readable memory which, when the plug-in module is attached, allows electronic interconnection between the electronics of the network node and the readable memory. The readable memory stores a unique node identifier which becomes associated with the node, and can also store functional program code for the particular node. Thus, a node can be easily and rapidly replaced or reprogrammed, without the need for specialized equipment to download the node identifier or functional program code, and without the possibility of erroneous manual entry of the node identifier. In operation, the node reads in its node identifier from the appropriate address of the readable memory, and thereafter sends and receives communications in accordance with the node identifier it has read out from the plug-in module. In one embodiment, the plug-in module takes the form of an enclosed cylindrical unit having wrapped about its periphery at one end a cylindrical attachment piece with inner threading, which connects to a threaded extension on the node housing. Pins along the base of the plug-in module fit snugly into opposing holes along the top of the extension piece on the node housing, or vice versa. The network node with plug-in module is particularly well suited for use in large, distributed control network systems, such as a multi-bus hierarchical control network.

RELATED APPLICATION INFORMATION

This application is a continuation of U.S. application Ser. No.09/442,369, filed on Nov. 17, 1999, hereby incorporated by reference asif set forth fully herein.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The field of the invention pertains to methods and apparatus forimplementing a control network and, more particularly, to a network nodefor use in a control network.

2) Background

Automated control systems are commonly used in a number ofmanufacturing, transportation, and other applications, and areparticularly useful to control machinery, sensors, electronics, andother system components. For example, manufacturing or vehicular systemsmay be outfitted with a variety of sensors and automated electricaland/or mechanical parts that require enablement or activation whenneeded to perform their predefined functions. Such systems commonlyrequire that functions or procedures be carried out in a prescribedorder or with a level of responsiveness that precludes sole reliance onmanual control. Also, such systems may employ sensors or othercomponents that require continuous or periodic monitoring and thereforelend themselves to automated control.

As the tasks performed by machinery have grown in number and complexity,a need has arisen for ways to exercise control over the variouscomponents of a system rapidly, efficiently and reliably. The sheernumber of system components to be monitored, enabled, disabled,activated, deactivated, adjusted or otherwise controlled can lead todifficulties in designing and implementing a suitable control system. Asthe number of system components to be controlled is increased, not onlyis the operation of the control system made more complicated, but alsothe wiring and inter-connections of the control system are likewise moreelaborate. In addition, greater reliance on automated control hasresulted in larger potential consequences if the automated controlsystem fails.

Certain conventional types of distributed control network use ahierarchical control structure with nodes to handle local tasks. Forexample, one type of control network uses a dual-bus architectureincluding a primary bus for a high-speed, bi-directional communicationlink interconnecting a main (or first-tier) data bus controller withdistributed slave nodes. One of the slave nodes acts as a second-tierdata bus controller connected to a secondary, low-speed data bus. Anumber of second-tier slave nodes may be connected to the secondary databus. The first-tier and second-tier slave nodes may be connected tovarious input/output ports for performing various local functions. Themain data bus controller, secondary data bus controller, first-tierslave nodes, second-tier slave nodes, input/output ports and othersystem components collectively form a hierarchical system wherein themain data bus controller supervises the first-tier slave nodes,including the second data bus controller, the second data bus controllersupervises the second-tier slave nodes, and the first-tier slave nodesand second-tier slave nodes supervise their assigned input/outputfunctions.

A more elaborate control network system as conventionally known isdescribed, for example, in U.S. Pat. No. 5,907,486, assigned to theassignee of the present invention. In the system described therein,additional data buses may be added to the hierarchical control network,so as to form additional second-tier control loops each having asecondary data bus controller (master node) and a set of second-tierslave nodes, and/or additional lower-tier control loops, each having anNth-tier data bus controller (master node) and a set of Nth-tier slavenodes.

A problem that particularly affects large, distributed control networksis re-configuring the system when network nodes are replaced or added. Anetwork node may be replaced because it has failed electrically, orbecause additional functionality is needed, or may be added to increasethe capability or size of the control network. Each network noderequires a unique identifier, so it can be referenced by the othernodes. Each network node is also required to be programmed with itsspecific functionality. As currently practiced, when network nodes arereplaced, a computer or special tool is needed to download the nodeidentifier and/or functional program code to the node. This taskrequires specialized equipment, and is time-consuming and inconvenient.Moreover, a mistake can be made in entering the node identifiermanually, which will cause the system to function improperly thereafter.

Likewise, when an existing network node needs to be reprogrammed tochange its functionality, the same sort of specialized equipment isneeded to download the new program or change the program parameters.Again, this task is time-consuming and inconvenient.

Accordingly, it would be advantageous to provide a mechanism forallowing rapid and convenient association of a network node with a nodeidentifier, and rapid and convenient programming of a newly added orexisting network node.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a network node for use in acontrol network is provided, in which association of a node identifierand/or functional program code with the node is carried out in a rapidand convenient manner, without the need for specialized equipment, andwithout the possibility of erroneous manual entry of the nodeidentifier.

In one embodiment, a network node includes a housing in which theelectronics of the network node are contained, including one or moreprocessors and various I/O functions. The housing includes a port towhich a plug-in module can be physically attached. The plug-in modulecontains a readable memory which, when the plug-in module is attached tothe node housing, allows electronic interconnection between theelectronics of the network node and the readable memory. The readablememory stores a unique node identifier which becomes associated with thenode, as well as, if desired, the functional program code for theparticular node. In operation, the node reads in its node identifierfrom the appropriate address of the readable memory, and thereaftersends and receives communications in accordance with the node identifierit has read out from the plug-in module.

In one embodiment, the plug-in module takes the form of an enclosedcylindrical unit having wrapped about its periphery at one end acylindrical attachment piece with inner threading. The node housing mayhave a short, cylindrically-shaped extension with outer threading forreceiving the cylindrical attachment piece. The cylindrical attachmentpiece may be screwed onto the cylindrically-shaped extension to securethe plug-in module to the node housing. When the plug-in module issecure, pins along the base of the plug-in module fit snugly intoopposing holes along the top of the extension piece on the node housing(or vice versa).

The network node configurations are described with reference to apreferred multi-bus hierarchical control network, which includes afirst-tier common bus and a plurality of lower-tier common buses. Afirst-tier master node controls a plurality of first-tier slave nodesusing the first-tier common bus for communication. Each of thefirst-tier slave nodes may be connected to a separate second-tier commonbus, and each operates as a respective second-tier master node for aplurality of second-tier slave nodes connected to the particularsecond-tier common bus associated with the first-tier slave/second-tiermaster node. Likewise, each of the second-tier slave nodes may beconnected to a separate third-tier common bus, and each would thenoperate as a respective third-tier master node for a plurality ofthird-tier slave nodes connected to the particular third-tier common busassociated with the second-tier slave/third-tier master node. Apreferred node comprises two separate transceivers, an uplinktransceiver for receiving control information, and a downlinktransceiver for sending out control information. Each node therefore hasthe capability of performing either in a master mode or a slave mode, orin both modes simultaneously.

Further variations and embodiments are also disclosed herein, and aredescribed hereinafter and/or depicted in the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a distributed control network with two data busesas known in the prior art.

FIG. 2 is another diagram of a distributed control network having a twodata buses each configured in a loop configuration as known in the priorart.

FIG. 3 is a circuit block diagram of a node that may be employed in thedistributed control network of FIG. 1 or FIG. 2.

FIG. 4 is a diagram showing a physical encasement of the node shown inFIG. 3.

FIG. 5 is a block diagram of a preferred control network architecture inaccordance with one or more aspects of the present invention.

FIG. 6 is a block diagram of a preferred node within the control networkarchitecture shown in FIG. 5.

FIG. 7 is a diagram of a hierarchical control network in accordance withone embodiment of the present invention having multiple second-tierbuses.

FIG. 8 is a diagram of a hierarchical control network in accordance withanother embodiment of the present invention having a third-tier bus.

FIG. 9 is a functional diagram of a multi-bus control networkillustrating one example of bus architectural layout and nodefunctionality according to one embodiment of the invention.

FIG. 10 is a diagram of a node housing illustrating attachment of aplug-in module.

FIG. 11 is a conceptual diagram illustrating electrical connection ofthe readable memory within a plug-in module to the electrical componentsof the node.

FIG. 12 is a conceptual diagram illustrating electrical connection ofthe readable memory within a plug-in module to the electrical componentsof the node, in accordance with an alternative embodiment as describedherein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

This application is generally related to U.S. Pat. No. 5,907,486entitled “Wiring Method and Apparatus for Distributed Control Network,”U.S. patent application Ser. No. 08/854,160 filed in the name ofinventor Jeffrey Ying, entitled “Backup Control Mechanism in aDistributed Control Network,” U.S. patent application Ser. No.08/853,893 filed in the name of inventors Jeffrey Ying and MichaelKuang, entitled “Fault Isolation and Recovery In A Distributed ControlNetwork,” and U.S. patent application Ser. No. 08/53,989 filed in thename of inventor Jeffrey Ying, entitled “Multi-Tier Architecture forControl Network,” all of which foregoing are hereby incorporated byreference as if set forth fully herein.

FIG. 1 is a block diagram showing the interconnection of nodes in aparticular type of control network 101 as known in the art. The controlnetwork 101 comprises a main data bus controller 103 which is connectedover a main data bus 104 to a plurality of first-tier slave nodes 109and 123. One first-tier slave node 123 connected to the main data bus104 also functions as a second data bus controller, and is connected toa second data bus 113. The second data bus controller 123 is connectedover the second data bus 113 to a plurality of second-tier slave nodes130. The main data bus 104 forms a high-speed, bi-directionalcommunication link between the main data bus controller 103 and thefirst-tier slave nodes 109 and 123, and the second data bus 113 forms alow-speed, bi-directional communication link between the second data buscontroller 123 and the second-tier slave nodes 130.

The nature of the slave nodes 109, 123 and 130 depends in part on thecontrol application for which they are deployed. In a transit vehicle orrailcar, for example, the master data bus controller 103 and the slavenodes 109, 123 and 130 may each be assigned to control a particularsection of the vehicle or railcar, or may be assigned to controlparticular input and output functions. For each slave node 109, 123 and130 in FIG. 1, various control signals are shown connected to the nodessuch as to illustrate one exemplary arrangement of controlfunctionality.

In operation, the main controller 103 communicates with the first-tierslave nodes 109 and 123 using the main data bus 104 as a high speedbi-direction link. An exemplary baud rate for communications over themain data bus 104 is 256 k. The main data bus controller 103 isgenerally responsible for delegating control commands to the first-tierslave nodes 109 and 123, and for responding to status information andevents communicated to the main data bus controller 103 over the maindata bus 104. Each of the first-tier slave nodes 109 and 123 receivescommands from the main data bus controller 103, and issues appropriatecommands over their respective control lines. In a similar manner, thesecond data bus controller 123 communicates with the second-tier slavenodes 130 using the second data bus 113 as a low speed bi-direction link(having a baud rate of, e.g., 9.6 k), and instructs the second-tierslave nodes 130 to carry out certain control functions, or responds tostatus messages or events relayed to the second data bus controller 123from the second-tier slave nodes 130.

FIG. 2 is a diagram showing the layout or architecture of the FIG. 1control network. The control network 201 shown in FIG. 2 comprises amain data bus controller 203 which is connected to a main data bus 204.The main data bus 204 is physically connected to a plurality offirst-tier slave nodes 209 and 223. As explained with respect to thecontrol network 101 shown in the FIG. 1, one of the first-tier slavenodes 223 also functions as a second data bus controller 223, and isconnected over a second data bus 213 to a plurality of second-tier slavenodes 230. The main data bus 204 is configured in a loop such that itpasses through each of the first-tier slave nodes 209 and 230 andreturns to rejoin the main data bus controller 203. In this way, shouldthe wires of the main bus 204 become severed, the main data buscontroller 203 will still be connected to the first-tier slave nodes 209and 223 and will not necessarily lose control over the system.Similarly, the second data bus 213 is configured in a loop such that itpasses through each of the second-tier slave nodes 230 and returns torejoin the second data bus controller 223, thereby providing anarchitecture resilient to potential severing of the wires of the seconddata bus 113. Each of the main data bus controller 203, first-tier slavenodes 209 and 223, and second-tier slave nodes 230 may be connected to aplurality of control signals for performing control or sensor functions,or various other input and output functions as necessary for theparticular control application.

The control network 201 shown in FIG. 2 thus utilizes a dual-busarchitecture to perform control functions. Because of the hierarchicalarchitecture of the control system 201, relatively low baud rates on thesecond data bus 213 can be tolerated, leading to reduced system size,cost and complexity over traditional non-hierarchical, relay-basedsystems. The slower speed on the secondary data bus 213 also reduces thesystem's susceptibility to electromagnetic interference, a potentialproblem in certain control system environments (such as railcars).

Each node, whether master data bus controller 203, first-tier slave node209 or 223, or second-tier slave node 230, includes means for performingcomputations necessary for its functionality, and is configured withcomponents such as a central processing unit (CPU) and memory. FIG. 3 isa more detailed block diagram of a node 301 (such as the master data buscontroller 203, a first-tier slave node 209 or 223, or a second-tierslave node 230) that may be employed in the control network of FIG. 2.The node 301 comprises a CPU 315 connected to a power control block 317and a transceiver 305. The node 301 is also connected to power signallines 316, which connect to the power control block 317. The node 301may communicate over communication signal lines 304, which are connectedto the transceiver 305. An electrical erasable programmable read-onlymemory (EEPROM) 306 stores programming information utilized by the CPU315 for carrying out certain programmable functions. The CPU 315 hasaccess to a random access memory (RAM) (not shown) and read-only memory(ROM) (not shown) as needed for the particular application.

The CPU 315 is connected to a keyboard and display interface block 320.The keyboard and display interface block 320 is connected to status LEDs307, relays 321, and LED display 311 and a keypad 331. The node 301 isthereby can accept manual inputs (e.g., from the keypad 331) or receivesensor inputs (e.g., over relays 321), and can display operationalstatus using status LEDs 301 or LCD display 311.

The node 301 further comprises a network controller 322 which preferablycomprises a second CPU. The network controller 322 is connected to asecond transceiver 323 which is connected to a second pair ofcommunication signal lines 314. The network controller also outputspower signal lines 336.

In operation, node 301 may communicate over two different data busesusing transceivers 305 and 323. Thus, node 301 may communicate over afirst data bus (such as data bus 204 shown in FIG. 1) by receiving andtransmitting signals over communication signal lines 314 usingtransceiver 323, under control of the network controller 322. The node301 may communicate over a second data bus (such as data bus 213 shownin FIG. 2) by transmitting and receiving signals over communicationsignal lines 304 using transceiver 305, under control of CPU 315. TheCPU 315 and network controller 322 may transfer information back andforth using a shared memory (not shown). The node 301 may serve as botha “slave” unit with respect to the first data bus 204 and a “master”unit with respect to the second data bus 213. By interconnecting aplurality of nodes 301 in an appropriate configuration, a hierarchicalcontrol network with two data buses (as shown in FIG. 2) may beestablished.

Each node 301 such as shown in FIG. 3 is housed in a rugged, potted casemade of a suitable lightweight material such as aluminum that providesenvironmental protection and allows for heat dissipation. FIG. 4 is adiagram showing an exemplary physical casing 401 of a module or node 301such as shown in FIG. 3. The casing 401 can be quite small; in theexample of FIG. 4, the casing 401 measures approximately 2.1′ by 3.75′,and is 0.825′ in thickness.

A problem that can occur in operation of a control network such as shownin FIG. 2 is that if the master data bus controller 203 fails thenoperation of the entire system could be jeopardized. A possible solutionwould be to provide a redundant master data bus controller that has thesame functionality as the primary master data bus controller 203 in allrespects. Upon detecting a failure of the primary master data buscontroller 203, the backup master data bus controller could shut downthe primary master data bus controller 203 and take over control of thenetwork.

While having such a separate, redundant master data bus controller forbackup purposes may provide a solution where the primary master data buscontroller 203 fails, it falls short of being a complete solution. As anentirely separate controller having complete functional and hardwareredundancy of the primary master data bus controller 203, incorporationof the backup master data bus controller effectively doubles the cost ofimplementing the master data bus controller 203. Also, another drawbackis that if both the master data bus controller 203 the backup masterdata bus controller fail, then operation of the entire system would bejeopardized and operation could come to complete halt.

In addition to the possibility of the master data bus controller 203failing, the second data bus controller 223 could also be subject tofailure. While a redundant second data bus controller for backuppurposes could be provided, the cost of implementing the second data buscontroller would be essentially doubled, and the system is still subjectto potentially complete failure should the second data bus controlleralso fail. Moreover, adding redundant data bus controllers couldcomplicate the wiring of the system.

A preferred embodiment of the invention overcomes one or more of theabove problems by providing redundant backup control for the master databus controller 203 or other type of master node, the second data buscontroller 223 or similar types of nodes, and, if further nested controllevels exist (as described, for example, in later embodiments herein),other sub-controllers for those control levels.

FIG. 5 is a block diagram of a preferred embodiment of a control network501 having redundant backup control capability for a master node at eachbus level of the control network 501. Hereinafter, the node acting asthe master bus controller for a particular bus will be referred to asthe “master node” for that particular bus, and all the other nodes onthat bus will be referred to as “slave nodes” for that particular bus.In the control network shown in FIG. 5, a master node 503 and aplurality of first-tier slave nodes 523 are connected to a main data bus504. In a preferred embodiment of the invention, each of the slave nodes523 is configured or can be configured to control a secondary data bus.For example, the first-tier slave node 523 c is shown connected to asecondary data bus 523 in the control network 501. The first-tier slavenode 523 c functions as a second-tier master node with respect tosecond-tier slave nodes 533 connected to the secondary data bus 513.Others of the first-tier slave nodes 523 can also serve as second-tiermaster nodes and be connected to different secondary buses havingadditional second-tier slave nodes. A multi-level or multi-tieredhierarchical control network is thereby established.

Each of the master node 503, first-tier slave nodes 523, second-tierslave nodes 533, and other lower-level slave nodes (not shown in FIG. 5)are referred to hereinafter generically as “nodes” and are designated asnodes 530 in FIG. 5. In one aspect of a preferred embodiment as shown inFIG. 5, each of the nodes 530 has substantially the same hardwareconfiguration and can therefore function as either a master node or aslave node, depending upon how the control network 501 is configured.Each data bus, along with the nodes attached to it, are generallyreferred to as a cell, and the master node connected to the data bus isreferred to as a “cell controller” for that particular cell. Asexplained in more detail hereinafter, each node 530 configured as amaster node transmits and receives messages over the data bus for thecell it controls. Each node 530 configured as a slave node remains in alisten mode, receiving but not transmitting messages over that data bus,unless specifically requested to transmit information over the data busby the master node. Any number of the slave nodes can, even thoughoperating as a slave node with respect to an upper tier, besimultaneously operating as a master node with respect to otherlower-tier slave nodes at a different cell sub-level.

A preferred embodiment of the invention, as noted, comprises a mechanismfor redundant backup control of any node functioning as a master node atany level or sub-level of the control network 501. As generallydescribed, in operation of a preferred embodiment of the invention theslave nodes connected to a particular data bus monitor the data buswhile in a listen mode and await periodic signals from the master nodefor that data bus. Upon a failure to receive a signal from a master nodewithin an expected time, the slave nodes connected to that data busbegin a wait period (which is preferably a different wait period foreach slave node connected to the data bus). When the wait periodelapses, the slave node determines that a failure in the master node forthe particular data bus has occurred, and takes steps to take over thefunctionality of the master node. Each of the slave nodes is programmedwith a different wait period, so that there is no contention forreplacing the master node when a master node failure has occurred. Inone aspect, backup control of each master node is prioritized, such thatthere is a specific order in which the slave nodes can potentially takeover control of the master node functionality when a failure hasoccurred.

In more detail, again with reference to FIG. 5, one of the nodes 530attached to the main data bus 504 is configured as a master node 503.The other nodes 530 attached to the main data bus 504 (in this examplenumbering four such nodes 530) are configured as first-tier slave nodes523, meaning that they receive but do not transmit master-controlsignals over the main data bus 504. The first-tier slave nodes 523 may,however, from time to time send responsive signals or status signalsover the main data bus 504.

In a preferred embodiment, each of the first-tier slave nodes 523 may beconfigured as a second-tier master node controlling a secondary bus. Onesuch example is shown in FIG. 5, wherein first-tier slave node 523 c isconnected to a secondary data bus 513. A plurality of other nodes 530are also attached to the secondary bus data 513, and serve assecond-tier slave nodes 533. There are three such second-tier slavenodes 533 in the example shown in FIG. 5. With respect to the secondarydata bus 513, the first-tier slave/second-tier master node 523 ctransmits master-control signals to the second-tier slave nodes 533. Thesecond-tier slave nodes 533 ordinarily operate only in a listen mode,but from time to time may send responsive messages or status messages tothe second-tier master node 523 c. The other first-tier slave nodes 523a, 523 b and 523 d may similarly be connected as second-tier masternodes (i.e., cell controllers) each controlling its own secondary bus orcell.

While the control network 501 shown in FIG. 5 has four first-tier slavenodes 523 and three second-tier slave nodes 533, the number offirst-tier slave nodes 523 and second-tier slave nodes 533 is limitedonly by the ability of the master node to communicate with the slavenodes over the particular data bus. There may be more slave nodes orfewer slave nodes on each bus than shown in the control network 501. Ina preferred embodiment, there are no more than eight such cellcontrollers, although more than eight may be used so long as processingcapacity and speed permit.

In addition, further levels of control nesting beyond two data buses mayalso be provided, using a similar approach to the two data bus method.Thus, for example, one or more of the second-tier slave nodes 533 may beconfigured as a third-tier master node controlling its own tertiary orthird-tier data bus. While FIG. 5 only shows two nested control levels,the same control concepts would apply to a control network architecturehaving additional nested control levels. Examples of control networkshaving more than two data buses are depicted in FIGS. 7, 8 and 9 anddescribed in more detail hereinafter.

In a preferred embodiment, communication over the main data bus 504 andthe secondary data bus 513 (or buses, if appropriate) istime-multiplexed such that only one node 530 is transmitting over aparticular data bus at a given time. Usually, each transmitted messagewill be targeted for a specific destination node 530, which may bespecified by address bits in the transmitted message. However, in someembodiments broadcast messages may also be used targeted to multiplenodes 530.

Responsibilities for tasks, or groups of tasks, may be assigned tospecific nodes 530. For example, each of the first-tier slave nodes 223may be assigned a distinct sphere of responsibility. Similarly, each ofthe second-tier slave nodes 533 may be assigned a distinct sphere ofresponsibility. Examples of tasks that may be assigned to differentnodes 530 are described for an exemplary control network later herein,with respect to FIG. 9.

Each of the nodes 530 preferably comprises an uplink transceiver 507, adownlink transceiver 508, and a switch 509. Each of the nodes 530receives signals over its downlink transceiver 508. Over the main databus 504, the first-tier master node 503 transmits master-control signalsto each of the first-tier slave nodes 523. From time to time, accordingto the programmed control protocol, the first-tier slave nodes 523respond to the master-control signals, or otherwise send status messagesto the first-tier master node 503 when events occur specific to thatfirst-tier slave node 523. Otherwise, the first-tier slave nodes 523 donot ordinarily communicate with each other.

In a similar manner, over each secondary data bus (such as secondarydata bus 513), the second-tier master node 523 (for example; first-tierslave/second-tier master node 523 c in FIG. 5) transmits master-controlsignals to each of the second-tier slave nodes 533 connected to the samesecondary data bus. From time to time, according to the programmedcontrol protocol, the second-tier slave nodes 533 respond to themaster-control signals, or otherwise send status messages to thesecond-tier master node 523 c when events occur specific to thatsecond-tier slave node 533. Otherwise, the second-tier slave nodes 523do not ordinarily communicate with each other.

Communication between nodes is preferably carried out using half-duplextime division multiplexing. In typical operation, the master node pollseach of the slave nodes periodically. Each of the nodes is preferablyprovided with a unique node identification number or address thatdistinguishes it from all other nodes of the control network. The masternode sends a control message to each slave unit in turn, using the nodeidentification number or address to identify the intended destination.Each of the slave nodes receives the control message but only reacts ifit recognizes its own node identification number or address in thecontrol message. The slave node takes the actions requested by thecontrol message received from the master node. Within a designated timeperiod after receiving the control message, the slave node responds tothe master node with an acknowledgment message. Each of the slave nodesare polled in turn so that the master node can keep track of eventshappening throughout the system.

A communication protocol is preferably established so as to avoidcollisions on each of the data buses. A simple and effectivecommunication protocol is one in which the master node for theparticular data bus sends a control message to a particular slave node,which responds with an acknowledgment or status message within apredetermined amount of time before the master node contacts anotherslave node. Slave nodes generally do not initiate communication withoutbeing first polled by the master node. The master node may also send outa broadcast control message that is intended for receipt by more thanone of the slave nodes. The broadcast control message can comprise anode identification number or address that instructs a single particularnode to respond to the broadcast control message. Usually, the singlenode selected for response will be the most critical node requiringreceipt of the broadcast control message.

Failure of the current master node (at any of the control levels)commonly results in the master node either failing to transmit, or elsetransmitting improper control information to the slave nodes over thedata bus. According to a preferred redundant backup control protocol,the slave nodes periodically receive master-control messages from themaster node and, in the event that proper master-control messages failto appear, initiate a failure mode response procedure.

Detection of and response to a failure mode condition may be explainedin greater detail with reference to FIG. 6, which is a block diagram ofa preferred embodiment depicting most of the main components of a node(such as any of nodes 530 shown in FIG. 5). Because failure modedetection and response is carried out by a node 530 operating as a slavenode, the following discussion will assume that the node 603 shown inFIG. 6 is initially configured as a slave node. Further, for simplicityof explanation, it will be assumed that the node 603 shown in FIG. 6 isa first-tier slave/second-tier master node connected to a main bus and asecondary bus (such as first-tier slave/second-tier master node 523 cconnected to the main data bus 504 and secondary data bus 513 in FIG.5), although the same node circuit configuration is preferably used foreach of the nodes 530, regardless of control level, for ease ofconstruction and flexibility purposes.

In the node block diagram of FIG. 6, a node 603 is shown connected to afirst bus (e.g., main bus) 604. The node 603 comprises an uplinktransceiver 611, a downlink transceiver 621, a CPU 612 connected to theuplink transceiver 611, and another CPU 622 connected to the downlinktransceiver 621. Both CPUs 612, 622 are preferably connected to adual-port RAM 618, and each CPU 612, 622 is connected to a ROM programstore 614 and 624, respectively. The second CPU 622 is connected throughan appropriate interface to I/O ports 654, which may comprise sensorinputs, control signal outputs, status LEDs, LCD display, keypad, orother types of external connections. It will be understood that the node603 of FIG. 6 can have all the components and functionality of the node301 shown in FIG. 3; however, in FIG. 6 only certain basic componentsneeded for explaining the operation of the invention are depicted.

Each node 603 is preferably capable of both sending and receivingmessages (e.g., control instructions). Typically, the uplink transceiver611 operates in a “slave” mode whereby the node 603 receives controlinstructions using the uplink transceiver 611 and then responds thereto,and the downlink transceiver 621 operates in a “master” mode whereby thenode 603 issues control instructions (e.g., polls slave nodes) andawaits a response from other nodes after sending such controlinstructions.

The downlink transceiver 621 of the node 603 is connected to a secondarydata bus 652, to which is also connected a plurality of second-tierslave nodes 651 (assuming the node 603 is a first-tier slave/second-tiermaster node). The node 603 thereby functions as a first-tier slave nodewith respect to the main data bus 604, receiving with its uplinktransceiver 611 first-tier master-control signals over the main bus 604from a first-tier master node (such as master node 503 shown in FIG. 5),and also functions as a second-tier master node with respect to thesecondary data bus 652, transmitting second-tier master-control signalswith its downlink transceiver 634 to second-tier slave nodes 651.

The node 603 also comprises a pair of switches 635 a, 635 b connectedbetween the downlink transceiver 621 and the signal lines 643 a, 643 bof the main data bus 604. In normal operation, the switches 635 a, 635 bremain open (unless the node 503 is also the first-tier master node,such as master node 503 shown in FIG. 5, in which case the switches 635a, 635 b would be closed), and the downlink transceiver 621 is therebyisolated from the main data bus 604. However, when a first-tier masternode failure condition is detected, switches 635 a, 635 b are closed,enabling the downlink transceiver 621 to take over for the first-tiermaster node. The downlink transceiver 621 would therefore functionsimultaneously as master node with respect to both the main data bus 604and the secondary data bus 652.

In a preferred embodiment, detection of a master node failure conditionon the main data bus 604 is accomplished using a timer mechanism, suchas a hardware timer 613 accessible (either directly or indirectly) bythe CPU 612 that is connected to the uplink transceiver 611. Accordingto a preferred control protocol (assuming the node 603 is a first-tierslave/second-tier master node), the uplink transceiver 611 of node 603receives first-tier master-control signals periodically from thefirst-tier master node (such as master node 503 in FIG. 5). Themaster-control signals may, for example, request status information fromthe node 603, or instruct the node 603 to carry out certain control orinput/output functions. The node 603 ordinarily responds by carrying outthe requested functions and/or sending an acknowledgment or statussignal to the first-tier master control node using the uplinktransceiver 611.

Timer 613 times out a wait period between master-control signalsreceived from the first-tier master control node. In a preferredembodiment, each time the uplink transceiver 611 receives amaster-control signal from the first-tier master node that is recognizedas an appropriate master-control signal within the particular programmedcontrol protocol (whether or not the master-control signal is directedto the particular node 603), the CPU 612 connected to the uplinktransceiver 612 resets the timer 613. If the timer 613 ever times out,then CPU 612 responds by asserting a failure mode response procedure.The timing out of timer 613 may result in an interrupt to CPU 612 inorder to inform the CPU 612 of the failure to receive master-controlsignals, or else the CPU 612 may periodically monitor the timer 613 and,when the CPU 612 notices that the timer 613 has timed out, assert afailure mode response procedure.

When a failure mode condition is detected, the CPU 612 sets a failuremode status bit in a predetermined flag location within the dual-portRAM 618. The other CPU 622 periodically monitors the failure mode statusbit in the dual-port RAM 618 and is thereby informed when a failureoccurs. Alternatively, instead of the CPUs 612, 622 communicatingthrough the dual-port RAM 618, timer 613 can directly inform CPU 622when a failure to receive master-control signals has occurred (i.e.,when timer 613 has timed out).

When the CPU 622 has been informed or otherwise determined that afailure mode condition exists, and that the first-tier master node haspresumably failed, the CPU 622 sends a signal over control line 633 toclose switches 635 a, 635 b, thereby connecting the downlink transceiver621 to the main bus 604. From that point on, the CPU 622 performs as thefirst-tier master node with respect to the main bus 604. The node 603can continue to receive information over the main data bus 604 using theuplink transceiver 611. Alternatively, the node 603 may thereafterperform all transmission and reception over both the main bus 604 andthe secondary bus 652 using the downlink transceiver 621. When thefailure mode is entered, the CPU 622 may be programmed so as to directlycarry out the I/O port functions for which it previously receivedinstructions from the first-tier master node, or the node 603 may sendmaster-control signals to its own uplink transceiver 611 and therebycontinue to carry out the I/O port functions as it had previously beendoing. In other words, the node 603 can give itself control instructionsover the main data bus 604 so that it can continue to perform itspreviously assigned functions. If, after taking over for the first-tiermaster node, the node's downlink transceiver 611 should fail, the node603 can still continue to perform its control functions when the nextslave node takes over control as the new first-tier master node (aslater described herein), because its uplink transceiver 611 continues tofunction in a normal manner.

According to the above described technique, the node 603 therebysubstitutes itself for the first-tier master node upon the detection ofa first-tier master node failure as indicated by the failure to receivethe expected first-tier master-control signals. Should the node 603fail, either before or after taking over control for the first-tiermaster node, the next first-tier slave node would take over and becomethe first-tier master node in a similar manner to that described above.

Referring again to FIG. 5, the order in which the first-tier slave nodes523 take over for the first-tier master node 503 is dictated by the waitperiod timed out by the timer 613 of the particular first-tier slavenode 523. The timer 613 (see FIG. 6) for each first-tier slave node 523is programmed or reset using a different time-out value. A first-tierslave node 523 only asserts a failure mode condition when its internaltimer 613 reaches the particular timeout value programmed for thatparticular node 523.

While the programmed wait periods for the internal timer 613 in eachfirst-tier slave node 523 can vary depending upon the controlapplication, illustrative wait periods are programmed in ten millisecondincrements. Thus, for example, first-tier slave node 523 a could beprogrammed with a 10 millisecond wait period; the next first-tier slavenode 523 b could be programmed with a 20 millisecond wait period; thenext first-tier slave node 523 c could be programmed with a 30millisecond wait period; and the last first-tier slave node 523 d couldbe programmed with a 40 millisecond wait period; and so on. First-tierslave node 523 a would take over as the first-tier master node if 10milliseconds elapses without it receiving any proper first-tiermaster-control signals; the next first-tier slave node 523 b would takeover as the first-tier master node if 20 milliseconds elapses without itreceiving any proper first-tier master-control signals; the nextfirst-tier slave node 523 c would take over as the first-tier masternode if 30 milliseconds elapses without it receiving any properfirst-tier master-control signals; and so on.

Use of 10 millisecond increments for the wait periods in the aboveexample is considered merely illustrative, and the actual wait periodsshould be selected depending upon the time criticality of the controlmessages, and the number of messages that may be missed before a highenough degree of certainty is established that the master node hasfailed. For example, if a slave node expects to observe acontrol-message signal on the data bus no later than every 5milliseconds, then the slave node may be programmed to assert a failuremode condition after a wait period corresponding to the absence of apredefined number of messages—for example, twenty messages (i.e., 100milliseconds). If critical aspects of the system requiring master nodecontrol need to be serviced in a shorter time period, then the waitperiod would have to be reduced to accommodate the time-sensitivecomponents of the system.

The order in which the slave nodes take over for the master node neednot be dictated by the relative position in the control loop of theslave node with respect to the master node, but rather may be dictatedaccording to the programmed wait period in each slave node. Flexibilityis thereby provided in the order of priority in which the slave nodestake over for the master node in the event of a failure event.

Accordingly, by use of the inventive techniques described herein,redundant backup for the first-tier master node 503 is provided. Suchredundant backup control is provided without requiring additionalphysical nodes to be located within the control system, and withouthaving to provide wiring for such additional physical nodes to the buses504 or 513. The redundant backup for the master node 504 is alsoaccomplished while resolving contention problems that might otherwiseoccur if each of the first-tier slave nodes 523 were programmed with theidentical timeout period.

In a preferred embodiment, redundant backup control is provided in asimilar manner for the secondary data bus 513, and each additional databus that may be provided in the system (e.g., in systems such as shownin FIGS. 7, 8 or 9). Thus, each of the second-tier slave nodes 533 ispreferably configured with the circuitry shown for node 603 in FIG. 6,and each of the second-tier slave nodes 533 can therefore substituteitself for the first-tier slave/second-tier master node 523 c if thefirst-tier slave/second-tier master node 523 c fails.

If a particular node is operating as a master node for two buses as aresult of a failure of the master node on a higher-tier bus, and thenode operating as such fails, then it is possible that two differentnodes will take over for the failed node, one node taking over on eachbus. For example, supposing that first-tier slave/second-tier masternode 523 c has already taken over as the first-tier master node due to afailure of the master node 503, and further suppose that first-tierslave/second-tier master node 523 c too fails, then the next first-tierslave node 523 d would take over as the first-tier master node withrespect to the main data bus 504, but the first second-tier slave node533 a would take over as second-tier master node with respect to thesecondary data bus 513.

In the above manner, despite the failure of one or more nodes,substantial functionality of the control system as a whole can bemaintained. A failed node is essentially discarded or bypassed to theextent possible so as to maintain the highest possible degree ofcontinued operability. Furthermore, because certain parts of the systemwill continue operate despite the failure of the master node,identification of the failed node by engineers or maintenance personnelshould be simplified by being able to identify the inoperative portionof the system that has become isolated due to the failure.

In one aspect, separation of responsibility in each node 603 of masterfunctions and slave functions between two different CPU's each operatingwith a different transceiver allows the node 603 to potentially continueoperating as either a master node or a slave node should one of theCPU's fail, providing that the failure does not disrupt both of thetransceivers at the node 603.

In a preferred embodiment, the nodes 530 of FIG. 5 are wired using asingle cable connecting all of the nodes 530 in a loop configuration.Details of such a wiring technique are described in U.S. Pat. No.5,907,486 entitled “Wiring Method and Apparatus for Distributed ControlNetwork,” assigned to the assignee of the present invention, andpreviously incorporated herein by reference.

In a preferred embodiment, the nodes 530 of FIG. 5 are configured withfault isolation and recovery circuitry in the case of a short circuit orsimilar event. Details of such fault isolation and recovery circuitryare described in copending U.S. application Ser. No. 08/853,893 entitled“Fault Isolation and Recovery In A Distributed Control Network,”previously incorporated herein by reference.

FIGS. 7, 8 and 9 depicts various embodiments having more than two databuses, so as to provide additional levels of control beyond thatafforded by a dual-bus architecture. Each of the nodes shown in FIGS. 7,8 and 9 is preferably configured to include the circuitry shown forpreferred node 603 in FIG. 6. FIG. 7 shows an example of a systemarchitecture for a control network having three data buses 704, 714 and724. A first-tier master node 703 and a plurality of first-tier slavenodes 712 are connected to the main data bus 704. One of the first-tierslave nodes 712, designated as A1 in FIG. 7, operates as a second-tiermaster node, and is connected to the second data bus 714 along with aplurality of second-tier slave nodes 722. Another of the first-tierslave nodes 712, designated as D1 in FIG. 7, operates as anothersecond-tier master node, and is connected to the third data bus 724along with another plurality of second-tier slave nodes 732. The otherfirst-tier slave nodes 712, designated B1 and C1 in FIG. 7, could alsobe configured as master nodes of a second-tier bus. FIG. 7 therebyprovides a hierarchical control network 701 having two control levels ortiers, and three data buses.

FIG. 8 shows an example of a system architecture for a control networkhaving four buses 804, 814, 824 and 834. In a similar manner to FIG. 7,a first-tier master node 803 and a plurality of first-tier slave nodes812 are connected to the main data bus 804. One of the first-tier slavenodes 812, designated as A1 in FIG. 8, operates as a second-tier masternode, and is connected to the second data bus 814 along with a pluralityof second-tier slave nodes 822. Another of the first-tier slave nodes812, designated as D1 in FIG. 8, operates as another second-tier masternode, and is connected to the third data bus 824 along with anotherplurality of second-tier slave nodes 832. One of the second-tier slavenodes 832 connected to the third data bus 824, denoted as A2′ in FIG. 8,operates as a third-tier master node with respect to the fourth data bus834, which is connected to a plurality of third-tier slave nodes 842.FIG. 8 thereby provides a hierarchical control network 801 having threecontrol levels or tiers, and four data buses.

It will be appreciated that, expanding the approach used in FIGS. 7 and8, additional control levels may be created by adding successive lowercontrol tiers, or additional slave nodes at any particular tier may beconfigured as cell controllers to control additional localized databuses. A great deal of flexibility is thereby provided in establishing ahierarchical control structure suitable for many different controlapplications.

FIG. 9 is a diagram showing, from a functional standpoint, an example ofa particular control application having multiple data buses inaccordance with the hierarchical control principles discussed herein. InFIG. 9, a control network 901 comprises a master node 904 which isconnected to a plurality of slave nodes 923, 924, 925 and 926, each ofwhich is assigned a particular sphere of responsibility within thecontrol network. A main bus 903 forms a communication link between themaster node 904 and the slave nodes 923, 924, 925 and 926.

Generally, the nature of the slave nodes 923, 924, 925 and 926 dependsin part on the control application in which they are deployed. In theexample of FIG. 9, the slave nodes 923, 924, 925 and 926 are deployed ina vehicle or railcar, and so the slave nodes 923, 924, 925 and 926 havefunctionality suited for such a control application. For example, theslave nodes include a slave node 923 operating as a rear sectioncontroller, a slave node 924 operating as a central section controller,a slave node 925 operating as a front section controller, and a slavenode 926 operating as a panel controller. There may also be additionalslave nodes if required.

Each of slave nodes 923, 924, 925 and 926 are considered first-tierslave nodes in the illustrative embodiment shown in FIG. 9. In thecontrol network 901 of FIG. 9, two of the first-tier slave nodes 923,924 also act as second-tier master nodes for additional data buses.Thus, first-tier slave node 923 operates as a second-tier master nodewith respect to a second data bus 913, and first-tier slave node 924operates as a second-tier master node with respect to a third data bus914. First-tier slave/second-tier master node 923 is connected to aplurality of second-tier slave nodes 931, 932, 933 and 934, which mayeach be assigned a sub-sphere of responsibility in the cell controlledby the rear section controller. The second-tier slave nodes maytherefore include, for example, a slave node 931 operating as atransmission controller, a slave node 932 operating as an engine sensorand controller, a slave node 933 operating as an air conditionercontroller, and a slave node 934 operating as a light indicatorcontroller.

Similarly, first-tier slave/second-tier master node 924 is connected toanother plurality of second-tier slave nodes 941, 942 and 943, each ofwhich may be assigned a sub-sphere of responsibility in the cellcontrolled by the central section controller. The second-tier slavenodes may therefore include, for example, a slave node 941 operating asa rear door controller, a slave node 942 operating as a lightcontroller, and a slave node 943 operating as a magnetic breakercontroller.

Each of the first-tier slave nodes 923, 924, 925 and 926 (even ifoperating as a second-tier master node) may be connected to one or moreinput/output modules 930. For example, the slave node 925 operating as afront section controller may be connected to a front door control module951, a kneeling mechanism control module 952, a wheel chair platformcontrol module 953, and a headlight output module 954. Likewise, theslave node 926 operating as a panel controller may be connected to anindicator module 961, an instrument module 962, a control switch module963, and other miscellaneous modules 964. Virtually any type ofinput/output or control function may represented as a module 930. Ineach instance, the respective slave node 923, 924, 925 and 926 controlsthe input/output modules 930 connected to it.

The master node 904 may be connected to a computer 907 through aninterface 906 (such as an RS-232 interface), if desired. Through thecomputer 907, the master node 904 can be instructed to execute certainfunctions or enter certain control modes. Also, the master node 904 canbe monitored or reprogrammed through the computer 907.

In operation, the master node 904 communicates with the cell controllers923, 924, 925 and 926 using the main bus 903. The master node 904, aspreviously described, is generally responsible for delegating controlcommands to the slave nodes 923, 924, 925 and 926, and for responding tostatus information and events communicated to the master node 904 overthe main bus 903. Each of the slave nodes 923, 924, 925 and 926 receivescommands from the master node 904, and issues appropriate commands totheir respective second-tier slave nodes 931-934 or 941-943, orinput/output modules 930.

Generally, the slave nodes are disposed in physical locations near themechanisms which they control. The main data bus 904 and secondary databuses 913, 914 each form a loop connecting the various nodes connectedto the bus in a continuous fashion. The data buses 904, 913 and 914 arenot restricted to any particular baud rate. Rather, communication may becarried out over each data bus 904, 913 and 914 at a rate that issuitable for the particular control application. Moreover, there is noparticular requirement that the data buses in the FIG. 9 control network(or the more generalized control networks shown in FIGS. 7 and 8) beserial data buses. Rather, the data buses may be parallel data buses insituations, for example, where a high data bandwidth is required.

In the particular control application relating to FIG. 9, each of thenodes is preferably housed in a rugged, potted case made of a suitablelightweight material such as aluminum that provides environmentalprotection and allows for heat dissipation, as previously described withrespect to FIG. 4. In other control environments, other types ofhousings may be used.

FIG. 10 is a diagram of a network node 1002 including a node housing1005 to which a plug-in module 1012 may be attached. The network node1002 may be used in any of the exemplary hierarchical control networksdescribed previously herein, or in any other type of control network inwhich it is required to replace or reprogram existing network nodes. Byuse of the plug-in module 1012, association of a node identifier and/orfunctional program code with the network node 1002 may be carried out ina rapid and convenient manner, without the need for specializedequipment, and without the possibility of erroneous manual entry of thenode identifier.

According to a preferred embodiment, as depicted in FIG. 10, the networknode housing 1005 contains the electronics of the network node 1002,including one or more processors and various I/O functions. In apreferred embodiment, the electronics within the network node housing1005 are similar to that depicted in FIG. 6, and are described in moredetail below with respect to FIG. 11. With respect to the physicalfeatures of the network node 1002 depicted in FIG. 10, the network nodehousing 1005 includes an external port 1008 to which the plug-in module1012 can be physically attached. In one embodiment, the plug-in module1012 takes the form of an enclosed cylindrical unit having a cylindricalmodule body 1020 containing electrical components. Wrapped about theperiphery of the cylindrical module body 1020, at one end, is acylindrical attachment piece 1021 having an inner threading 1025. Theexternal port 1008 of the network node housing 1005 may take the form ofa relatively short, cylindrically-shaped extension as shown in FIG. 10,with an outer threading 1007 for receiving the cylindrical attachmentpiece 1021. The cylindrical attachment piece 1021 is rotatable, and maybe screwed onto the cylindrically-shaped extension (i.e., external port1008) to secure the plug-in module 1012 to the node housing, in themanner as is commonly done to fasten certain types of plastic pipingtogether, for example.

In one embodiment, the external port 1008 comprises an arrangement ofpins 1006 protruding upwards, emanating from the top of the externalport 1008. The plug-in module body 1020 includes a matching arrangementof holes 1023 for receiving the pins 1006. When the plug-in module 1012is secure fastened to the node housing 1005, the pins 1006 atop theexternal port 1008 fit snugly into the holes 1023 along the base of theplug-in module fit 1012. Alternatively, the pins could be located on thebase of the plug-in module body 1020, while the holes would then belocated atop the external port 1008 on the node housing 1005.

As further shown in FIG. 10, cables 1030 and 1031 forming a portion ofthe continuous, common bus are inserted into the node housing 1005, toallow the node 1002 to be included as part of a network such as depictedin any of FIG. 2, 7, 8 or 9, for example.

In a preferred embodiment, the plug-in module 1012 contains a readablememory which, when the plug-in module 1012 is attached to the nodehousing 1005, allows electronic interconnection between the electronicsof the network node housing 1005 and the readable memory. Details ofpreferred electronics, at a block diagram level, are illustrated in FIG.11. As shown therein, a preferred network node 1102 may comprise many ofthe same electrical components as illustrated for the node in FIG. 6.Thus, the network node housing 1105 may contain, among other things, anuplink transceiver 1111, a downlink transceiver 1121, a CPU 1117connected to the uplink transceiver 1111, and another CPU 1122 connectedto the downlink transceiver 1121. Both CPUs 1117, 1122 are preferablyconnected to a dual-port RAM 1118, and each CPU 1117, 1122 may beconnected to a ROM program store 1114 a and 1124, respectively. Thesecond CPU 1122 is connected through an appropriate interface to I/Oports 1154, which may comprise sensor inputs, control signal outputs,status LEDs, LCD display, keypad, or other types of externalconnections. It will be understood that the node 1102 of FIG. 11 canhave all the components and functionality of the node 301 shown in FIG.3; however, in FIG. 11 only certain components are depicted for the sakeof simplicity.

Similar to node 603 in FIG. 6, the node 1102 is preferably capable ofboth sending and receiving messages (e.g., control instructions).Typically, the uplink transceiver 1111 operates in a “slave” modewhereby the node 1102 receives control instructions using the uplinktransceiver 1111 and then responds thereto, and the downlink transceiver1121 operates in a “master” mode whereby the node 1102 issues controlinstructions (e.g., polls slave nodes) and awaits a response from othernodes after sending such control instructions. The downlink transceiver1121 may be connected to a secondary data bus, to which may also beconnected a plurality of lower-tier slave nodes.

The node 1102 may also comprise a pair of switches 1134 connectedbetween the downlink transceiver 1121 and the signal lines and busconnector 1142, the purpose of which has been described in detail abovewith reference to FIG. 6. A timer mechanism, such as timer 613accessible to CPU 1117, may be used to detect a master node failurecondition on the main data bus connected to the bus connector 1142.

A preferred communication protocol for the node 1102 within a controlnetwork system involves the ability to identify each node 1102 with aunique identifier. Communication between nodes may be carried out, forexample, using half-duplex time division multiplexing, wherein themaster node polls each of the slave nodes periodically. Each of thenodes is preferably provided with a unique node identification number oraddress that distinguishes it from all other nodes of the controlnetwork. The master node sends a control message to each slave unit inturn, using the node identification number or address to identify theintended destination. Each of the slave nodes receives the controlmessage but only reacts if it recognizes its own node identificationnumber or address in the control message. The slave node takes theactions requested by the control message received from the master node.Within a designated time period after receiving the control message, theslave node responds to the master node with an acknowledgment message.Each of the slave nodes are polled in turn so that the master node cankeep track of events happening throughout the system.

To facilitate identification of the node 1102, the readable memory 1114contained within the plug-in module 1112 stores a unique node identifierwhich becomes associated with the node 1102 when the plug-in module 1112is secured to the module housing 1105. The readable memory 1114 isdefined within the address space of the node 1102. Once the plug-inmodule 1112 is connected, the CPU 1117 accesses the node identifier atthe address provided for the readable memory 1114, and uses the nodeidentifier in subsequent communication activities. The CPU 1117 may, forexample, determine which messages are targeted to the node 1102, and mayinsert the node identifier in messages transmitted from the node 1102.The CPU 1117 may share the node identifier with the second CPU 1122 byloading into the dual-port RAM 1118, at a specified location.

In addition, the readable memory 1114 may also include functionalprogram code for the node 1102. The CPU 1117 may be programmed so thatit first attempts to utilize the functional program code, if any, storedin the readable memory 1114, and if then secondarily attempts to utilizethe functional program code stored in the program ROM 1114 a. Thefunctional program code stored in the readable memory 1114 may be sharedwith the second CPU 1122 if desired by downloading it to the dual-portRAM 1118.

Accordingly, the node 1102 may be programmed or re-programmed with aunique node identifier and functional program code simply by connectingor replacing the plug-in module 1112, avoiding the need to download anode identifier or functional program code from specialized equipment,and increasing the speed and convenience by which a node 1102 can beprogrammed or re-programmed.

The readable memory 1114 may contain any type of persistent data memory,including read-only memory (ROM), programmable ROM (PROM), orelectrically-erasable programmable ROM (EEPROM), for example.

FIG. 12 is a conceptual diagram illustrating electrical connection ofthe readable memory within a plug-in module to the electrical componentsof the node, in accordance with an alternative embodiment as describedherein. The components illustrated in FIG. 12 are generally analogous tothose shown in FIG. 11. Thus, network node 1202 may comprise a networknode housing 1205 which may contain, among other things, an uplinktransceiver 1211, a downlink transceiver 1221, a CPU 1217 connected tothe uplink transceiver 1211, and another CPU 1222 connected to thedownlink transceiver 1221, operating in a manner similar to thatdescribed for FIG. 11. Both CPUs 1217, 1222 are preferably connected toa dual-port RAM 1218, and each CPU 1217, 1222 may optionally beconnected to a ROM program store 1214 a and 1224, respectively. Thesecond CPU 1222 is connected through an appropriate interface to I/Oports 1254, which may comprise sensor inputs, control signal outputs,status LEDs, LCD display, keypad, or other types of externalconnections, as described with respect to FIG. 11.

The main difference between the node 1102 depicted in FIG. 11 and thenode 1202 depicted in FIG. 12 is that the node 1202 depicted in FIG. 12has a second electrical connection directly from the readable memory1214 of the plug-in module 1212 to the second CPU 1222, so that thesecond CPU 1222 can obtain direct access to the unique node identifieras well as any functional program code stored in the readable memory1214. The readable memory may be partitioned, or may physically comprisetwo separate memory chips, to avoid conflicts between the two CPU's 1217and 1222 in accessing the information stored in the readable memory1215. In all other respects, operation of the node 1202 of FIG. 12 isessentially the same as the node 1102 depicted in FIG. 11.

From the standpoint of physical construction, the node housing 1005 (or1105 or 1205) may comprise a rugged, potted case made of a suitablelightweight material such as aluminum that provides environmentalprotection and allows for heat dissipation.

The plug-in module 1012 (or 1112 or 1212) can take a wide variety ofalternative forms. It may be of any other shape that is convenient, suchas rectangular, square, or polygonal. Likewise, the external port 1008may be in the form of an inset, cavity or depression rather than anextension, with the plug-in module 1012 inserting snugly inside theport. Further, the plug-in module 1012 may be fastened to the nodehousing 1005 by other suitable means besides using an encapsulatingthreaded screw mechanism as shown in FIG. 10. For example, the plug-inmodule 1012 may snap into the node housing 1005, or may have one or morescrews externally attached (similar to many common computer printercables) to the plug-in module body 1020, which may be screwed in tocorresponding holes in the node housing 1005. The particular plug-inmodule 1012 depicted in FIG. 10 provides the advantage of ease of manualattachment to the node housing 1005, as well as giving a very secure andstable connection. For applications in which the plug-in module 1012needs to be particularly small, a snap-on fastening mechanism may bepreferred.

While preferred embodiments are disclosed herein, many variations arepossible which remain within the concept and scope of the invention.Such variations would become clear to one of ordinary skill in the artafter inspection of the specification and drawings herein. The inventiontherefore is not to be restricted except within the spirit and scope ofany appended claims.

1. A network node for use in a control network, comprising: a nodehousing, said node housing comprising an external port; a processorcontained within said node housing; a transceiver contained within saidnode housing, said transceiver having a connection for an external databus; a detachable module adapted for connection to said external port,said detachable module comprising an enclosed module body; and areadable memory encapsulated within said enclosed module body, saidreadable memory storing a unique node identifier for the network node;wherein said readable memory is accessible to said processor when saiddetachable module is connected to said external port. 2-31. (canceled)